Leaf C:N:P stoichiometric homeostasis of a Robinia pseudoacacia plantation on the Loess Plateau

Homeostasis is the adaptability of a species to a changing environment.However,the ecological stoichiometric homeostasis of Robinia pseudoacacia L.in diff erent climatic regions is poorly understood but could provide insights into its adaptability in the loess hilly region.This study sampled 20 year-old R.pseudoacacia plantations at 10 sites along a north–south transect on the Loess Plateau.Variations in the ecological stoichiometric characteristics of leaf and soil carbon,nitrogen,and phosphorus were analysed and homeostatic characteristics of leaf ecological stoichiometric parameters in diff erent climates were identifi ed.Factors aff ecting leaf stoichiometry were assessed.The results show that R.pseudoacacia leaves were rich in nitrogen and defi cient in phosphorous during tree growth and development.Nitrogen and phosphorous levels in the soils of the loess region were lower than the average in soils in the rest of China.All ecological stoichiometric parameters of R.pseudoacacia leaves in two diff erent climates were considered“strictly homeostasis”.Precipitation,available phosphorus,and soil C:P were the main factors aff ecting the variation of C:N:P stoichiometry of R.pseudoacacia leaves.R.pseudoacacia in the loess hilly region has strong ecologically homeostatic characteristics and suggests that it is well-adapted to the area.

Seasonal variations of leaf traits and drought adaptation strategies of four common woody species in South Texas, USA

Understanding physiological responses and drought adaptation strategies of woody plant leaf traits in sub-humid to semi-arid regions is of vital importance to understand the interplay between ecological processes and plant resource-allocation strategies of different tree species.Seasonal variations of leaf morphological traits,stoichiometric traits and their relationships of two drought tolerant woody species,live oak(Quercus virginiana)and honey mesquite(Prosopis glandulosa)and two less drought tolerant species,sugarberry(Celtis laevigata)and white ash(Fraxinus americana)were analyzed in a sub-humid to semi-arid area of south Texas,USA.Our findings demonstrate that for the two drought tolerant species,the leguminous P.glandulosa had the highest specific leaf area,leaf N,P,and lowest leaf area and dry mass,indicating that P.glandulosa adapts to an arid habitat by decreasing leaf area,thus reducing water loss,reflecting a resource acquisition strategy.While the evergreen species Q.virginiana exhibited higher leaf dry mass,leaf dry matter content,C content,C:N,C:P and N:P ratios,adapts to an arid habitat through increased leaf thickness and thus reduced water loss,reflecting a resource conservation strategy in south Texas.For the two less drought tolerant deciduous species,the variations of leaf traits in C.laevigata and F.americana varied between Q.virginiana and P.glandulosa,reflecting a trade-off between rapid plant growth and nutrient maintenance in a semi-arid environment.

Dynamics of forest biomass carbon stocks from 1949 to 2008 in Henan Province,east-central China

We estimated forest biomass carbon storage and carbon density from 1949 to 2008 based on nine consecutive forest inventories in Henan Province,China.According to the definitions of the forest inventory,Henan forests were categorized into five groups: forest stands,economic forests,bamboo forests,open forests,and shrub forests.We estimated biomass carbon in forest stands for each inventory period by using the continuous biomass expansion factor method.We used the mean biomass density method to estimate carbon stocks in economic,bamboo,open and shrub forests.Over the 60-year period,total forest vegetation carbon storage increased from34.6 Tg(1 Tg = 1×10;g) in 1949 to 80.4 Tg in 2008,a net vegetation carbon increase of 45.8 Tg.By stand type,increases were 39.8 Tg in forest stands,5.5 Tg in economic forests,0.6 Tg in bamboo forests,and-0.1 Tg in open forests combine shrub forests.Carbon storageincreased at an average annual rate of 0.8 Tg carbon over the study period.Carbon was mainly stored in young and middle-aged forests,which together accounted for 70–88%of the total forest carbon storage in different inventory periods.Broad-leaved forest was the main contributor to forest carbon sequestration.From 1998 to 2008,during implementation of national afforestation and reforestation programs,the carbon storage of planted forest increased sharply from 3.9 to 37.9 Tg.Our results show that with the growth of young planted forest,Henan Province forests realized large gains in carbon sequestration over a 60-year period that was characterized in part by a nation-wide tree planting program.

Simulating the vegetation-producing process in small watersheds in the Loess Plateau of China

Small watersheds are the basic composition unit of the Loess Plateau in China. An accurate estimation of vegetation net primary productivity （NPP） is of great significance for eco-benefit evaluation in small watershed management in this region. Here we describe the development and testing of a vegetation-producing process model （VPP） of a small watershed in the Loess Plateau. The model couples three modules： radiation adjustment; soil hydrological processes; and vegetation carbon assimilation. Model validation indicates that the VPP model can be used to estimate the NPP of small watersheds in the region. With the VPP model, we estimated the spatial NPP distributions in the Yangou watershed for 2007. The results show that in the Yangou watershed the NPP is relatively low, averaging 168 g C/（m^2.a）. Trees and shrubs have a higher NPP than crops and grasses. The NPP is larger on the partly shaded and shaded slopes than on the partly sunny and sunny slopes. The NPP on the slopes increases gradually on 0-20° slopes and decreases slightly on slopes steeper than 20°. Our simulation indicates that the vegetation type is the most important factor in determining the NPP distribution in small watersheds in the Loess Plateau.

Pursuing the goal of carbon neutrality in China:path for realization of carbon sequestration in planted forests

Tree plantations are an important forest resource that substantively contributes to climate change mitigation and carbon sequestration.As the area and standing volume of tree plantations in China have increased,issues such as unreasonable structure,low productivity,limited ecological functionality and diminishing ecological stability have occurred,which hinder the ability of tree plantations to enhance carbon sequestration.This study outlined the trajectory of carbon sequestration and its associated benefits in tree plantations by examining the current state of tree plantation establishment and growth,elucidated the strategies for advantages of carbon sequestration and climate change mitigation in planted forests,and summarized the existing problems with tree plantations.This paper underscores the pressing need for concerted efforts to boost carbon sequestration within planted forests and proposes management and development strategies for Chinese tree plantations.In the future,it will be necessary to apply scientific theories to practice and develop multi-objective management optimization models for the high-quality development of tree plantations.This will involve establishing a cohesive national carbon trading market,improving the prediction of carbon sequestration,and identifying priority zones for afforestation and reforestation,to better serve China’s national strategy for achieving peak carbon and carbon neutrality.

Soil microbial respiration is regulated by stoichiometric imbalances: Evidence from a humidity gradient case

Humidity not only affects soil microbial respiration(SMR) directly, but, indirectly by regulating the availability of soil water and nutrients. However,the patterns of direct and indirect effects of humidity on SMR over large precipitation gradients remain unclear, limiting our understanding of the effects of precipitation changes on soil C cycle. Here, we investigated the relationships among humidity, soil nutrients, and SMR by identifying stoichiometric imbalances, microbial elemental homeostasis, and microbial C use efficiency along a precipitation gradient at a continental scale. The relationship between SMR and humidity index(HI) corresponded to a Richard’s curve with an inflection point threshold value of approximately 0.7. Soil microbial respiration increased with increasing humidity in drier areas(HI < 0.7), but tended to balance above this threshold. Increasing humidity exacerbated C:P and N:P imbalances across the selected gradient. Severe N and P limitations in soil microbial communities were observed in drier areas, while soil microbes suffered from aggravated P limitation as the humidity increased in wetter areas(HI > 0.7). Soil microbial communities regulated their enzyme production to maintain a strong stoichiometric homeostasis in drier areas;enzyme production, microbial biomass, and threshold elemental ratios were non-homeostatic under P limitation in wetter areas, which further contributed to the increase in SMR. Our results identified a moisture constraint on SMR in drier areas and highlighted the importance of nutrient(especially for P) limitations induced by humidity in regulating SMR in wetter areas. Understanding the modulation of SMR via soil enzyme activity may improve the prediction of soil C budget under future global climate change.

硫化氢在植物中的生理功能及作用机制

硫化氢(H_2S)是继一氧化氮(NO)和一氧化碳(CO)之后第3个气体信号分子,在植物体内参与许多重要的生理活动,能够促进植物光合作用和有机物的积累,缓解各种生物和非生物胁迫并促进植物生长发育。该文综述了植物体内H_2S的物理化学性质、产生机制、主要生理功能和作用机制以及与其它信号分子的互作关系,并展望了H_2S信号分子的研究前景。

HIGH QUALITY DEVELOPMENTAL APPROACH FOR SOIL AND WATER CONSERVATION AND ECOLOGICAL PROTECTION ON THE LOESS PLATEAU

The Loess Plateau is the core area in the Yellow River basin for implementing environmental protection and high-quality development strategies. A series of ecological projects has implemented aimed at soil and water conservation and ecological management on the Loess Plateau over the past 70 years. The effects of the ecological projects are apparent mainly through a marked increase in vegetation cover, controlled soil erosion and reduced flow of sediment into the Yellow River, continual optimization of the industrial structure and increased production from arable land, poverty alleviation and greater prosperity, and optimal allocation of space for biological organisms.Major problems have also been analyzed in ecological management including the fragile ecosystem of the region, maintaining the stability of vegetation,lower agricultural productivity and continued risk from natural disasters. Some suitable schemes and models have been developed for the coordinated development of the region through research and demonstration, striking the optimum balance between rural industry and ecology, and increased regionalcapacity to supply high-quality ecological products. Countermeasures to address the problems are suggested to guide ecological management and high-quality development in the future.

Stoichiometric homeostasis in response to variable water and nutrient supply in a Robinia pseudoacacia plant-soil system

All organisms need elements in fixed proportions for carrying out normal metabolic processes and how flexible they are depends on how effective they are utilizing these resources from external sources.It is important to understand the interactions among plant,soil and microbial biomass carbon(C),nitrogen(N)and phosphorus(P)stoichiometry under different conditions of resource supply.We conducted a pot experiment on 1-year-old Robinia pseudoacacia seedlings for nearly 5 months under different water,nitrogen and phosphorus supplies,and we determined plant,soil and microbial biomass C,N and P stoichiometry.We found that plant,soil and microbial nutrients and stoichiometry exhibited a certain degree of plasticity in response to the changes in water and nutrient conditions in their environments.Variation partitioning analysis showed that root stoichiometry accounted for a large part of the variance in microbial stoichiometry.Structural equation modeling further revealed that root stoichiometry and leaf stoichiometry were two direct factors affecting microbial biomass C:N and C:P,and that root stoichiometry had the greatest direct effect.In addition,the degree of homeostasis for microbial biomass C and C:P was more sensitive to changes in soil nutrients than changes in other factors,and other elements and elemental ratios displayed strict homeostasis.These results highlight the importance of studying microbial stoichiometry in improving our understanding of nutrient cycling of the plant-soil system under different water and nutrient supply.